Method of coding a plurality of audio signals

Abstract

In a method of coding a plurality of audio signals, the left and the right basic channel as well as the central channel are combined by joint stereo coding so as to obtain a jointly coded signal, which is decoded so as to provide simulated decoded signals. The simulated decoded signals and two surround channels are combined by matricization by means of a compatibility matrix so as to form compatible signals which are suitable for decoding by existing decoders. In order to avoid audible disturbances caused by excessive energy contents of the compatible signals, which would occur if joint stereo coding and decoding were carried out prior to carrying out the matricization, the compatible signals or the simulated decoded signals are dynamically weighted by means of a dynamic correction factor in such a way that the compatible signals are approximated with regard to their energy to the energy of signals which would be obtained if the two basic channels and the central channel as well as the surround channels were matricized directly.

We claim: 
     
       1. A method of coding a plurality of audio signals, comprising the steps of: combining at least two signals by joint stereo coding so as to obtain a jointly coded signal,   decoding the jointly coded signal so as to provide simulated decoded signals,   combining the simulated decoded signal and at least one additional signal so as to provide signals that are compatible with existing decoders, said simulated decoded signal and said at least one additional signal being combined in a compatibility matrix by matricizing, and   dynamic weighting of either the compatible signals or the simulated decoded signals by means of at least one dynamic correction factor so as to approximate the compatible signals with regard to their acoustically relevant signal properties to the signals which would be produced if these at least two signals and the additional signal were directly matricized by means of this compatibility matrix.   
     
     
       2. A method according to claim 1, wherein the step of dynamically weighting the compatible signals or the simulated decoded signals by means of the dynamic correction factor is carried out such that the compatible signals are, with regard to their energy, approximated to the energy of the signals which would be produced if these at least two signals and the additional signal were directly matricized by means of the compatibility matrix. 
     
     
       3. A method according to claim 1, wherein the step of joint stereo coding comprises jont stereo coding of the left and of the right basic channel and of the central channel, and wherein the additional signals correspond to the left and to the right surround channel. 
     
     
       4. A method according to claim 3, wherein the compatibility matrix is as follows:   Lc=a·L+b·C+c·Ls;       Rc=a·R+b·C+c·Rs;     wherein Ls and Rs stand for the left and right surround channels, L and R stand for the left and right basic channels, C stands for the central channel, a, b and c stand for the coefficient of the compatibility matrix and Lc, Rc stand for the compatible signals.   
     
     
       5. A method according to claim 1, wherein a single dynamic correction factor is calculated on the basis of the at least two signals, which are to be subjected to joint stereo coding, and on the basis of at least part of the simulated decoded signals, and wherein each of the simulated decoded signals is multiplied by this dynamic correction factor prior to its matricization. 
     
     
       6. A method of decoding the audio signals coded according to claim 5, wherein the correction factor is transmitted to the decoder,   the jointly coded signal is subjected to joint stereo decoding so as to obtain the decoded left and right basic channels as well as the decoded central channel,   the decoded left and right basic channels as well as the decoded central channel are weighted with the correction factor by multiplication, and   that the thus weighted signals are matricized together with the compatible signals by means of an inverse compatibility matrix so as to regain the left and right surround channels.   
     
     
       7. A method according to claim 6, wherein the single dynamic correction factor m is determined according to the following relationship: ##EQU3## wherein L and R stand for the left and right basic channels, C stands for the central channel, a and b stand for coefficients of the compatibility matrix, and L' and R' stand for simulated decoded right and left basic channels produced by joint stereo coding and joint stereo decoding. 
     
     
       8. A method according to claim 4, wherein two dynamic correction factors ml, mr are determined such that the following equations are fulfilled:   |a·L+b·C+c·Ls|.sup.2 =|ml·(a·L'+b·C')+c·Ls.vertline..sup.2       |a·R+b·C+c·Rs|.sup.2 =|mr·(a·R'+b·C')+c·Rs.vertline..sup.2     wherein Ls, Rs stand for the left and right surround channels, L and R stand for the left and right basic channels, C stands for the central channel, a, b and c stand for coefficients of the compatibility matrix, and Lc', Rc' stand for the compatible signals, and   the simulated decoded left channel obtained by joint stereo coding and subsequent joint stereo decoding as well as the simulated decoded central channel are weighted with one of the correction factors and the simulated decoded right channel obtained by joint stereo coding and subsequent joint stereo decoding as well as the simulated decoded central channel are weighted with the other correction factor prior to being matricized by means of the compatibility matrix together with the left and right surround channels so as to provide the compatible signals.   
     
     
       9. A method of decoding the audio signals coded according to claim 8, wherein the two correction factors are transmitted to the decoder,   the jointly coded signal is subjected to joint stereo decoding so as to obtain the decoded left and right basic channels as well as the decoded central channel,   the decoded left basic channel and the decoded central channel are weighted with one of the correction factors by multiplication and the decoded central channel as well as the decoded right basic channel are weighted with the other correction factor by multiplication, and   that the thus weighted signals are matricized by means of an inverse compatibility matrix together with the compatible signals so as to regain the right and left surround channels.   
     
     
       10. A method according to claim 4, wherein two dynamic correction factors kl, kr are determined such that the following equations are fulfilled: ##EQU4## wherein Ls, Rs stand for the left and right surround channels, L and R stand for the left and right basic channels, C stands for the central channel, a, b and c stand for coefficients of the compatibility matrix, and Lc', Rc' stand for the compatible signals, and wherein a respective one of the compatible signals, which are produced by matricization, is weighted by a respective one of the correction factors.   
     
     
       11. A method of decoding the audio signals coded according to claim 10, wherein the correction factors are transmitted to the decoder,   the compatible signals are divided by the correction factors; and   the thus weighted compatible signals are subjected to an inverse compatibility matrix together with the signals, which were obtained by joint stere decoding of the jointly coded signal, so as to provide the left and right surround channels.